Spark plug



1944- I J. G. JACKSON 2,355,163

SPARK PLUG Filed Oct. 18, 1940 INVENTOR ohn L3. Jackson tion of the plug.

Patented Aug. 8, 1944 SPARK PLUG John. G. Jackson, Detroit, Mich., assignor to Square D Company, Detroit, Mich, a corporation of Michigan Application October 18. 1940, Serial No. 361,684

3 Claims.

This invention relates to spark plugs for internal combustion engines, and more particularly to spark plugs for internal combustion engines of high output capacities,-such as aeroplane engines. o

In spark plugs as used on aircraft engines at the present time the construction generally used includes a wrapping of thin mica sheets about the central electrode stem and a built-up body thereabouts formed from mica discs forced together under relatively high pressures. Various wedging and other pressure applying means are used in order to make the resultant assembly gas tight. This has resulted in a very expensive spark plug which is not only difiicult to seal against gas leakage, but in which great care must be taken in assembly in order to secure the necessary dielectric strength.

The object of this invention is to obviate these difficulties and to produce an extremely simple, inexpensive and rugged spark plug for heavy duty use which shall have the necessary dielectric strength and which shall be sealed against gas leakage.

Another object of the invention is a provision of a spark plug in which the desired dielectric strength is obtained through the use of a fused vitreous enamel upon the central electrode stem and/or on the interior surface of the body por- Another object of the invention is a provision of a spark plug having the central electrode stem coated with a fused vitreous enamel and cemented in place in the body portion of the plug by a. cement which may be the same fused vitreous eieamel used in coating the central electrode s 111.

Another object of the invention is to provide a radio shielded spark-plug having a conducting tube extending above and about the central electrode stem, which tube has its interior surface coated with a fused vitreous enamel of high dielectric strength.

Another object of the invention ls to provide an improved construction of cooperating elec- Figure 2 is a bottom plan view of the spark Plug.

- Figure 3 is an enlarged fragmentary view showing the coating and sealing construction of the tube.

Figure 4 is a vertical sectional view similar to Figure 1 but showing an alternative plug con- I struction.

Figure 5 is 'a vertical sectional view similar to Figure 1 but showing a radio shielded type of plug.

The spark plug shown in Figures 1, 2- and 3 comprises a central electrode stem I having an electrode tip 2. which may be the same or a different material than the main portion of the stem, and a terminal connector 3 upon its upper end. The electrode stem is provided with a coating 4 of a fused vitreous enamel intimately adhering thereto and insulating the stem from the main body portion of the plug. This main body portion comprises a lower generally cylindrical portion 5 threaded at its lower end for reception in the cylinder block and interiorly threaded at its upper end to receive a second cylindrical portion 6 in which the electrode stem is cemented. The cylindrical portions 5 and 6 are provided with a metallic gasket I to prevent gas leakage. In the bottom of the cylindrical portion 5, a generally conical electrode element 8 is secured by pressing, welding, brazing, or any other desired means. This electrode'is generally in the form of an inverted truncated cone with the sides of the cone cut out at 9 to leave four electrode points ll. These points ll extend angularly toward the central electrode 2 and have their end surfaces parallel to the central electrode as at I! so as to present a considerable surface to the electrode at which the ignition spark may strike. This construction permits long life to the electrode points even under heavy duty conditions without materially disturbing the gap setting to an extent which would result in defective ignition.

Figure 3 shows an enlarged fragmentary view of the coating and sealing of the electrode to the body portion. The interior surface of the body portion is provided with a coating l3 of the same fused vitreous enamel as that used for coating the central electrode and the two coatings are then cemented together by a cement H. While this cement may take various forms according to the spirit of this invention, it has been found preferable to use the same vitreous enamel as that used in the coatings I and I3, these coatings and the binding fusing together into a substantiallyunitaryfusedmassasshown lungare 1.

This invention is not limited to any particular composition for the fused vitreous enamel used in the coating 4, as it is understood that any such enamel having ahigh dielectric strength which will adhere to the material of the central electrode stem and the temperature range to which it will be subjected in use may be used for the coating. For the cement I, where it is not the same vitreous enamel used in the coatinga 4 and I3; any fragmentary cement having sufllcient mechanical bonding powers and which is impervious to e of gases may be used. where a cement which is not impervious to the passage of gas would be desired, the end surfaces thereof may be sealed by the same vitreous enamel or any .other gas tight material which would adhere thereto.

The coating may be applied in any well known manner and many desired effective thickness. They can be applied as a single coating or may be built up from a plurality of coatings and are applied and fired in conventional manner. The relative proportions of the parts shown in the figures are, of course, entirely relative and may be varied as desired to increase or decrease the coating or cementing thicknesses.

The spark plug shown in Figure 4 is identical with that shown in Figure 1 except that the two cylindrical parts I and I have now been consolidated into a unitary body portion It, the other parts of the plug remaining the same. The plug of Figure 1 would be preferred where it would be desired to separate the body portion so as to have access to the body electrode I removed from the central electrode 2. n the other hand, if this separation is not deemed necessary, the single unitary body portion ll of Figure 4 would be used.

The spark plug of Figure 5 is of the radio.

shielded type and for the cylindrical portion 8 has been substituted a cylindrical portion I. having a tube extension H to which the shielding cover of the ignition cable may be attached, this tube being threaded at its upper end at II for this I attachment purpose. The interior surface of the tube H is provided with an insulating coating ll of the same fused vitreous enamel as is used for the coating 4 on the electrode stem, this coating having the necessary dielectric strength for electric insulating purposes. The other parts of this plug remain the same and it is to be understood that the invention is applicable to shielded or unshielded plugs with the additional inventive concept in the shielded plug of using the vitreous enamel for the dielectric coating of the shielding tube.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims:

What is claimed is:

l. A radio shielded spark plug comprising a body portion, a central electrode therein, and a shielding tube extending around and above said central electrode, said tube having an interior insulating coating of fused vitreous enamel.

2. In a radio shielded spark plug, a body portion carrying an electrode surface, a central electrode stem carrying an electrode surface cooperating with said first electrode surface to provide an arcing gap, an electrically insulating coating about said central electrode comprised of a fused vitreous enamel directly adhering thereto, a shielding tube extending around and above said central electrode, and a coating of fused vitreous enamel on the interior surface of said tube.

3. In a radio shielded spark plug for internal combustion engines, a body portion and a central electrode mounted therein, a gas tight fused vitreous enamel directly adhering to said central electrode, a body portion for supporting the central electrode in insulating relation with the body portion, a shielding tube extending around and above said central electrode, and a coating of fused vitreous enamel on the interior surface of said tube.

JOHN G. JACKSON. 

